Polishing of semiconductor wafers requires a polishing method which ensures the necessary polishing speed while preventing defects such as mechanical warping. In conventional mechanical polishing methods, the polishing speed can be ensured by increasing the size of the abrasive grits or the applied polishing load. However, because polishing results in various defects, it has been difficult to both ensure polishing speed and keep polishing targets defect-free. One method that has been proposed is known as chemical mechanical planarization (CMP). This method takes advantage of a chemical polishing action in addition to a mechanical polishing action, making it possible to both guarantee polishing speed and obtain defect-free polishing targets. With the higher integration of devices in recent years, CMP polishing of surfaces of semiconductor substrates having conductive metal layers formed on wafer surfaces has become important at certain stages in the production of integrated circuits.
One example of a metal CMP process is one that uses a polishing pad comprising a polyurethane resin, and a chemical slurry containing alumina particles as abrasive grits and iron nitrate as an oxidizing agent and prepared to have a pH of about 1.5 with nitric acid. For polishing, a semiconductor substrate is contacted with the polishing pad while circulating chemical slurry so that polishing is accomplished by relative rotation. Because the polishing speed is reduced at this time due to loading of the polishing pad, conditioning of the polishing pad is essential. Conditioning of a polishing pad has conventionally been accomplished by running water or chemical slurry over the polishing pad while a conditioner with nickel electrodeposited diamond abrasive grits is used to level the polishing pad.
The conditioner used for the CMP process differs from a conventional diamond tool used for cutting and grinding in essentially the following aspect. With cutting tools there is no loss of cutting power even if some shedding of the diamond abrasive grits occurs, so long as other diamonds are left on the new surface after the diamond shedding, whereas with a CMP conditioner, the shedded diamond abrasive grits damage the polishing pad or semiconductor substrate surface, and therefore diamond shedding is unacceptable even in small amounts. In addition, since wet systems are employed at a low rotation rate, there is no need for the heat resistance or high abrasion resistance demanded for cutting tools. Conventional diamond tools for which shedding of the diamond abrasive grits is a problem include diamond bits wherein single-grain, relatively large diamonds are bonded in a metal supporting material. However, these are essentially different from conditioners used in CMP processes in the following aspect. With conventional diamond bits, relatively large diamonds (generally with a diameter of about 1 mm or greater) are bonded as single grains, whereas conditioners used for CMP processes have relatively small (50-300 .mu.m diameter) diamonds bonded in a sheet-like manner in a single layer.
Conventional conditioning of a polishing pad has employed a conditioning method which uses a grinding stone having nickel electrodeposited diamond grains. Nickel electrodeposition has become widely used because it can be applied relatively easily to metal supporting materials. However, nickel is readily corroded by acid. Consequently, when nickel electrodeposited conditioners are employed for conditioning when using acidic slurry, corrosion of the nickel occurs because of the acidic slurry. As a result, the usable life of the conditioner is considerably shortened, scratch damage due to shedding of the diamond grains occurs within a shorter time, and the polishing speed is reduced because of deteriorating conditioning performance. For this reason there has been a demand for diamond conditioners with high durability against acidic slurry.